This invention relates to a dual stage process for the catalytic conversion of olefin(s) to provide ether(s). More particularly, the invention relates to a process for the catalytic conversion of a feed containing one or more light olefins such as ethylene, propylene, butenes, pentenes, hexenes, heptenes, etc., in a first stage in the presence of recycled ether(s) to provide a mixture of alcohol(s) and ether(s), the alcohol(s) being subsequently converted in a second stage, e.g., by reaction with light olefin or by catalytic distillation, to provide ether(s). The ether(s) are useful, inter alia, as high octane blending stocks for gasoline.
There is a need for an efficient catalytic process to manufacture ethers from light olefins thereby augmenting the supply of high octane blending stocks for gasoline. Lower molecular weight ethers such as diisopropyl ether (DIPE) are in the gasoline boiling range and are known to have a high blending octane number In addition, by-product propylene from which DIPE can be made is usually available in a fuels refinery. The petrochemicals industry also produces mixtures of light olefin streams in the C.sub.2 to C.sub.7 molecular weight range and the conversion of such streams or fractions thereof to ethers can also provide products useful as solvents and as blending stocks for gasoline.
The catalytic hydration of olefins to provide alcohols and/or ethers is a well-established art and is of significant commercial importance. Representative olefin hydration processes are disclosed in U.S. Pat. Nos. 2,162,913; 2,477,380; 2,797,247; 3,798,097; 2,805,260; 2,830,090; 2,861,045; 2,891,999; 3,006,970; 3,198,752; 3,810,849; and, 3,989,762, among others.
Olefin hydration employing zeolite catalysts is known. As disclosed in U.S. Pat. No. 4,214,107, lower olefins, in particular, propylene, are catalytically hydrated over a porous crystalline aluminosilicate, or zeolite, catalyst having a silica to alumina ratio of at least 12 and a Constraint Index of from 1 to 12, e.g., ZSM-5 type zeolite, to provide the corresponding alcohol, essentially free of ether and hydrocarbon by-product.
According to U.S. Pat. No. 4,499,313, an olefin is hydrated to the corresponding alcohol in the presence of hydrogen-type mordenite or hydrogen-type zeolite Y, each having a silica-alumina molar ratio of from 20 to 500. The use of such a catalyst is said to result in higher yields of alcohol than olefin hydration processes which employ conventional solid acid catalysts. Use of the catalyst is said to offer the advantage over ion-exchange type olefin hydration catalysts of not being restricted by the hydration temperature.
U.S. Pat. No. 4,783,555 describes an olefin hydration process employing a medium pore zeolite as hydration catalyst. Specific catalysts mentioned are Theta-1, said to be preferred, ferrierite, ZSM-22, ZSM-23 and NU-10.
Japanese Laid-Open patent application No. 60-246335 discloses the hydration of branched olefins to alcohols in the presence of a zeolite having a silica to alumina ratio of above 10.
The catalyzed reaction of olefins with alcohols to provide ethers is another well known type of process.
As disclosed in U.S. Pat. No. 4,042,633, diisopropyl ether (DIPE) is prepared from isopropyl alcohol (IPA) employing montmorillonite clay catalysts, optionally in the presence of added propylene.
U.S. Pat. No. 4,182,914 discloses the production of DIPE from IPA and propylene in a series of operations employing a strongly acidic cation exchange resin as catalyst.
In U.S. Pat. No. 4,334,890, a mixed C.sub.4 stream containing isobutylene is reacted with aqueous ethanol to form a mixture of ethyl tertiary butyl ether (ETBE) and tertiary butyl alcohol (TBA).
U.S. Pat. No. 4,418,219 discloses a process for preparing methyl tertiary butyl ether (MTBE) by reacting isobutylene and methanol in the presence of boron phosphate, blue tungsten oxide or a crystalline aluminosilicate zeolite having a silica to alumina mole ratio of at least 12:1 and a Constraint Index of from 1 to about 12 as catalyst.
As disclosed in U.S. Pat. No. 4,605,787, alkyl tertalkyl ethers such as MTBE and tertiary amyl methyl ether (TAME) are prepared by the reaction of a primary alcohol with an olefin having a double bond on a tertiary carbon atom employing as catalyst an acidic zeolite having a Constraint Index of from about 1 to 12, e.g., ZSM-5, ZSM-11, ZSM-12, ZSM-23 dealuminized zeolite Y and rare earth-exchanged zeolite Y.
U.S. Pat. No. 4,714,787 discloses the preparation of ethers by the catalytic reaction of linear monoolefins with primary or secondary alcohols employing, as catalyst, a zeolite having a pore size greater than 5 Angstroms, e.g., ZSM-5, zeolite Beta, zeolite X, zeolite Y, etc. Specifically, in connection with the reaction of propylene with methanol to provide methyl isoopropyl ether (MIPE), effluent from the reactor is separated into a MIPE fraction, useful as a gasoline blending component, with unreacted propylene, methanol, by-product dimethyl ether (DME) and water at up to one mole per mole of by-product DME, either individually or in combination, being recycled to the reactor.
In European patent application No. 55,045, an olefin is reacted with an alcohol to provide an ether, e.g., isobutene and methanol are reacted to provide MTBE, in the presence of an acidic zeolite such as zeolite Beta, ZSM-5, ZSM-8, ZSM-11, ZSM-12, ZSM-23, ZSM-35, ZSM-43 and ZSM-48, and others, as catalysts.
German Patent No. 133,661 describes the reaction of isobutene and methanol to provide a mixture of products including MTBE, butanol and isobutene dimer employing acidic zeolite Y as catalyst.
Japanese Laid-Open patent application No. 59-2534 describes the reaction of a primary alcohol with a tertiary olefin in the presence of a zeolite having a silica to alumina mole ratio of at least 10 and the X-ray diffraction disclosed therein to provide a tertiary ether.
It is also known to produce mixtures of alcohols and ethers in a dual stage process.
Thus, in accordance with the process described in U.S. Pat. No. 4,731,489, isobutene and methanol are reacted in a first stage reaction zone in the presence of an acidic ion-exchange resin-type catalyst to provide MTBE which, together with water and additional isobutene, is converted by hydration and etherification reactions, primarily the former, in a second stage reaction zone, also in the presence of an acidic ion-exchange resin-type catalyst, to provide mainly tertiary butyl alcohol and MTBE.